Slot antennas have been widely investigated over the past 60 years. Slot antennas can be divided into two groups: slot antennas in a screen and boxed-in slot antennas. Slot antennas in a screen are wideband antennas that radiate in two directions. Boxed-in slot antennas are narrow band antennas that radiate in only one direction. The narrow bandwidth of operation of boxed-in antennas is achieved by cutting a radiating slot in a wall of a resonant cavity tuned to resonate on the TE10 mode. The resonant cavity substantially increases the size of the antenna, even in a space saving configuration presented in U.S. Pat. No. 6,307,520, and makes the antenna narrowband. The prior art of slot antennas failed to combine in one design wide bandwidth of operation with the directional property of boxed-in slot antennas.